Production of plaster board



June 14, 1960 w. M. BROTHERS 2,940,505

PRODUCTION OF PLASTER BOARD Filed Oct. 12, 1953 IN VENT OR W ll/dldn )n.

- ATTORNEY United States Patent 2,940,505 PRODUCTION OF PLASTER BOARD Filed Oct. 12, 1953, Ser. No. 385,588 Claims priority, application Great Britain Oct. 16, 1952 2 Claims. (Cl. 154-1.2)

The present invention relates to the production of plaster board, that is to say building boards comprising a core of gypsum plaster lined on at least one and usually both faces with paper liners bonded to the plaster core.

The usual practice in the production of such boards is to feed and distribute a water-setting slurry of plaster of Paris between two sheets or strips of paper drawn continuously between a pair of rollers arranged one above the other and spaced apart by a distance corresponding to the thickness of the board to be produced, and moving the formed plaster and paper sandwich on a conveyor for a'period during which the plaster takes a set, and thereafter passing it through a heating and drying chamber usually after dividing the sandwich into desired lengths.

If attempts are made to apply two sheets of paper in the manner described above, to a core-forming slurry of neat plaster, or of plaster containing usual additions such as from agents used to reduce the weight of the boards, setting accelerators and the like, the bond produced between the plaster core and the paper in boards so produced is ineffective, the paper being readily parted from the set core.

In order therefore to obtain a satisfactory bond between the core and the paper it is the present practice to embody in the core-forming plaster slurry an adhesive usually of the nature of a starch, so that adhesion between the paper and the core is achieved. The need for such adhesives, however, involves a substantial addition to the cost of production of the board.

It has now been found that a very strong bond is obtained by first coating the paper sheet or sheets with a very thin layer of plaster on the surface thereof which is to be engaged with the core-forming plaster and thereafter bringing the thin coated surface or surfaces into contact with the core-forming plaster.

A very strong bond is obtained between the thin plaster layer and the paper even with no starch or other adhesive present in the plaster used to form the thin layer, and the thin layer when subsequently applied to the core-forming plaster combines therewith to form a homogeneous mass.

In some cases a small proportion of starch, gum or other adhesive may be embodied in the plaster used to form the thin layer, but the use of such an adhesive in the core-forming plaster is unnecessary.

It will thus be seen that the need for starch or other adhesive is wholly or largely eliminated by the use of the present invention.

The invention accordingly consists in a method of producing a plaster board, paper lined on one or both surfaces thereof, said method including the step of applying a thin layer of plaster to the surface of the paper-liner sheet or sheets intended to engage the core-forming plaster, as a preliminary to bringing the paper-liner sheet or sheets intoengagement with the core-forming plaster slurry.

The preliminary thin coating layer of plaster may be formed by pouring on and distributing over the paper sheet a cream obtained by pre-mixing plaster and water,

distribution or spreading being effected for example by drawing the paper over a flat smooth table and below a roller mounted above the table. I

Good results have been obtained making use of a solution of plaster in water and comprising as an example 70 parts by weight of water to parts by weight of neat plaster and such a cream may be spread by the use of upper lightly loaded chromium plated or other smooth surfaced spreading rollers to provide a thin plaster layer on the paper sheet of a few, e.g. seven, thousandths of a'n inch thick. In some cases however, two or more spreading rollers may be used in succession and the first of said rollers may be provided with surface projectionseg. left and right hand helical ridges to effect the preliminary spreading of the plaster cream.

The thus coated paper sheets may at any time, that is to say before or after the thin plaster coating has wholly set, be used in the production of the plaster board by bringing the thin-coated surface or surfaces into contact with the core-forming plaster slurry.

A lower or higher proportion of plaster than that named above can be used but with a higher proportion of plaster the spreading of the plaster cream to produce an even thin layer becomes more diflicult.

The improved method of producing plaster board is well adapted to be carried out as a continuous process and an apparatus for carrying out such a continuous process as applied to the production of plaster board paper lined on both sides, is illustrated by way of example in the accompanying drawing in which Fig. 1 is a view in side elevation of the part of the apparatus relevant to the present and Fig. 3 shows a detail.

Referring to the drawings, 1 and 2 represent two con-. paper drawn of? from supply reels tinuous webs of liner (not shown) and intended to form the upper and lower surface liners respectively of the plaster boards to' be produced.

Core plaster slurry is delivered in well known manner" on to the lower moving paper liner 2 by Way of a chute 3 having an outlet 4 disposed over the centre of the paper web 2. The core plaster slurry is supplied continuously to the chute 3 from a suitable source (not shown) by. means of an endless travelling band 5. v V

e web 2 with the core slurry thereon as indicated by 6 passes from below the chute 3 betweena pair of rolls 7 together with the upper liner web 1 and the' spacing of the rolls 7 is selected in accordance with the thickness of the plaster board to be produced.

The rate of feed of the core plaster slurry from the thickness over a width corresponding to that of the required plaster board product.

The formed sandwich indicated at 8 in Fig. 1, of core plaster 6 and paper webs 1 and 2 pass from the rolls 7 onto an endless conveyor 9 on which it remains until it is set to an extent to permit it to be cut into lengths and handled for subsequent treatment such as heating to complete the set, all in well known manner.

In accordance with the present invention two further delivery chutes 10 and 11 are mounted in positions in which the respective paper webs 1 and 2 are required to pass beneath the outlets 12 and 13 thereof before reaching the point of application to the core plaster 6.

The plaster cream is supplied to the two chutes 10 and 11 from a source or sources (not shown) by means of endless conveyors 14 and 15, and is delivered from the outlets 12 and 13 of the chutes 10 and 11 on to the longitudinal centres of those surfaces of the moving webs 1 plaster board-forming invention, Fig. 2 is al plan view of the part of the apparatus shown in Fig. 1

cated by 1 7, thereon pass I smooth surfaces and beneath a roller, or in the case'il- .lustrafed, tworollers 19' and 20 in succession mounted aboveythesurfaces of the tables 18 and resting by their v and 2 whieh are to be applied to the core-forming plaster slurry 6. Since in the case of the upper web 1 the side of the web which is to engage the core-forming plaster slurry 6 is ultimately the underside of that web, the said upperflweb 1 is led arounda guide roller 16 which in conjunction with the upper of the two squeeze rollers 'Z, efiectsareversal of the web 1, and the chute-'10 supplying ing of the cream likc mixt re of neat plaster and with the r coated faces of said sheets facing each other, and feeding a slurry. encore-forming plaster'h'etwe'enjs'aid sheets the plaster cream to the upper web 11 is located at-a point 7 precedingtheguide roller 16 as shown in the drawings when the sideiof the webl to which the plaster cream is to be applied is for the time being uppermost.

f Thepaperwebs land 2 with the plastercream in'diover tables 18 having fiat own weight orlightly loaded, upon the moving paper webs whereby the plaster cream is distributed orspread over the whole width of the webs 1 and 2.

The 'stance of-travel of the webs Land 2 between the chutes and 11 delivering the plaster cream and the chute 3, delivering the core-plaster lurry need only be sufiicient to enable the plaster. cream 17 to be effectively spread over the width of the paper webs before engagemerit is made with the core-plaster slurry 6. V

In. some cases the spreading roller or some or all of the spreading rollers for the plaster cream may with advantage be,provided with relief projections. onthe surface thereof. Such a roller isillustrated by way of example in Fig.3, the rollerhere shown being provided with right and left handhelically arranged ridges of small depth. 1 p

'The core f rming plaster used in the formation of plasterboard usually contains setting accelerators and the setting time for neat plaster as usually employed for the formation of the preliminary coating cream according to the present invention is long by comparison.

, -Iheslow setting of the neat plaster of the cream: before it co'mes into contact with the core-formingplaster, however,lpre's'ents no inconvenience but afiords timeffor better absorption or. penetrationof the neat.plaster of the cream into the paper webs before the recrystallisation takes place. f

" After'thepreliminary thin-coatingof plaster on the wcb s ha s been brought into contact with the core-forming plaster the early setting of the latter in itself induces an accelerationof; the setting'of -theplaster ofthe preliminary. coating.

What isclairned is: l f v I ,*1..,A method of producing plaster board which is paper-.lined-on both faces thereof, said method including thestepsof. pouring on one face of each paper-liner sheet at the point where they are brought into parallel relation. 2. Apparatus for the continuousproduction j :plas ter board formed of a plaster'core paper-linedon-lbdfll shrfaces, comprising a first chute for delivering corel-forming plaster slurry onto a lower liner-paper web, a pair of squeezing and-spreading'rolls between'which the said lower liner-paper web with the core-plaster ihfiI'BQIlqlEO- gether with an upper liner-paper Web are passed tofor m a sandwich of core-plaster between two liner-papers con- 'stituting the plaster board, two further chutes positioned one above each web at points preceding theentry of the two webs and the core-forming plaster slurry-between the said'squeezing and spreading rolls, a supply of a cream-like mixture of neat plaster in water feeding each of said two further chutes, and at least one spreading roller located between each one of the said two further chutes and said first chute and having rolling contact with said webs under light pressure for spreading the mixture of neat plaster and water from the said two fur. ther chutes into thin layers of um'form'thickness across the width of the liner-paper webs before said webs'comc into contact with core-forming plaster slurry, said-mix tore-applying chutes being positioned in advance-of said squeezing rolls, a distance to ensure at least partialiimpregnation of said sheets by said cream mixture upon reaching said squeezing rolls, a smooth-surfaced table arranged beneath each web and supporting said "webs after they leave the said two further chutes, the spread-.

, further chutes being provided on opposite endportions' acream-likemixture of neat plaster and water, subject:

ing the saidI-poured mixture to spreading under light pressure to form on the liner sheets ,very thin layers of .plaster cream :of uniform thickness of the order ofseven thousandths of an inch thick, and thereafter thereof with. left-hand and. right-hand helical ridges. respectlvely, said ridges constituting relief projections" which assist in spreading the neat plaster andwater mix-.

ture laterally from the central zone of-each web.

' References Cited in the fileof this'patent UNITED STATES PATENTS 1,428,827 Brookby Sept. 12', "1922" 1,459,264 Routt a. June 19,1192; 2,051,452 Mactag'gart'e't a1. Au .1s,'1936 2,088,813 Roos Aug. 3,1193?" 2,213,249 Kelley Sept.:3, 1940 

